1. Field of the Invention
The present invention relates to a thin film magnetic head, in particular, it relates to an improvement of a magnetic core configuration around a magnetic gap region for preventing magnetic saturation and reducing leakage flux.
2. Description of the Related Art
In the prior art, there is disclosed a thin film magnetic head in Japanese Patent Laid-open Publication 3-58308/1991 by the present applicant, wherein a closed magnetic circuit of a magnetic head core is constructed by an upper core, a lower core and intermediate cores interposed between the upper and lower cores. Each of these cores is embedded in an insulation layer to be flush therewith. Thus, it is possible to obtain a magnetic circuit having excellent magnetic properties by forming each of the cores in a pattern exactly using a thin film forming technique such as a photo-lithograph. It is noted that a side of the thin film magnetic head confronting a magnetic recording medium is referred to as a front side for convenience, and an opposite side of the front side is referred to as a rear side. Further, a side of a substrate is referred to as a lower side, and an opposite side of the lower side is referred to as an upper side hereafter.
FIG. 1(A) is a plan view showing a thin film magnetic head of the prior art, 1(B) is a sectional view taken along line #A--#A of FIG. 1(A) and FIG. 1(C) is a perspective view showing a construction of a magnetic core portion of FIGS. 1(A) and 1(B).
Referring to FIGS. 1(A)--1(C), a reference character 10 designates a substrate, and 12 a first insulating layer provided on the substrate 10. On the first insulating layer 10, a lower core 16 is formed surrounded by a second insulating layer 14 to be flush therewith. On the lower core 16, front intermediate cores 18, 20 and a rear intermediate lower core 22 and a rear intermediate upper core 24 are respectively stacked. A magnetic gap 26 made of non-magnetic material is provided between the front intermediate cores 18, 20. Further, coils 28, 29 are respectively embedded in a third insulator 13 and a fourth insulator layer 14 by causing them to be wound around the rear intermediate lower core 22 and the rear intermediate upper core 24. One of the distal ends of coils 28 and that of another coil 29 are connected to a connecting portion 35. Other distal ends of coils 28, 29 are respectively connected to lead wires 34. In FIG. 1(B), a reference character 30 designates a fifth insulator layer, however, it is not depicted in FIG. 1(A).
Thus, it will be understood from the above description that a magnetic head core 100 forming a magnetic circuit of the prior art comprises the lower and upper cores 16, 32, the front intermediate cores 18, 20, the magnetic gap 26 interposed between the lower and upper cores 16, 32 and the rear intermediate lower and upper cores 22, 24.
As shown in FIGS. 1(A) and (C), the upper core 32 generally comprises a rear portion 32a (a right-hand side) having a rectangular shape, a front portion 32b (a left-hand side) having a narrower rectangular shape than that of the rear portion 32a and an intermediate portion 32c having a pair of slanting parts interposed between the rear and front portions 32a and 32b in the plan view. The front portion 32b of the upper core 32 has the same width as a track width W along which signals are recorded on the recording medium. A reference character P designates an inflection point at which the intermediate portion 32c and the front portion 32b is connected. Thus, the width at the inflection point is the same as the track width W, because the inflection point P is in accordance with a root of the front portion 32b.
The lower core 16 has the same shape as that of the upper core 32, thus the detailed description of the lower core is omitted. The reference characters 16a, 16b and 16c respectively designate a rear portion, a front portion and an intermediate portion of the lower core 16.
Front intermediate cores 18, 20 are respectively provided on the front portions 16b, 32b in such a manner that rear distal ends of the front intermediate cores 18, 20 accord with the inflection points P. Further, in the plan view, areas of the front portions 16b, 32b are made substantially equal to attached areas of the front intermediate cores 18, 20.
As shown in FIG. 1(B), an overall thickness of the magnetic head core 100 within a range of a gap depth L defined from a contact surface of the recording medium to the inflection point P, is equal to the total sum of thicknesses of the lower and upper cores 16, 32 and of the front intermediate cores 18, 20.
Next, the description is given of the magnetic circuit of the magnetic head core 100.
FIG. 2(A) is an exploded perspective view showing a construction of a magnetic head core portion by separating an upper core from a lower core, FIG. 2(B) is a perspective view showing a cross-sectional area taking along a line X1, FIG. 2(C) is a perspective view showing a cross-sectional area taking along a line X2, FIG. 2(D) is a perspective view showing a cross-sectional area taking along a line X3, and FIG. 2(E) is a perspective view showing a cross-sectional area taking along a line X4.
As seen from FIGS. 2(B)-2(E), each of the cross-sectional areas defined by lines X1-X4 shows a cross-sectional area of the magnetic circuit of the magnetic head core 100. Comparing these cross-sectional areas of the magnetic circuit with one another, the cross-sectional area along the line X2 nearby the inflection point P is relatively the narrowest among these areas, thus it will be understood that the cross-sectional area along the line X2 is most easily magnetically saturated, which poses a degradation of a magnetic efficiency of the thin film magnetic head.
Next, a description is given to a magnetic leakage flux of the thin film magnetic head.
Referring to FIG. 3, generally, as well known, a magnetic flux 8 generated from an N pole of a magnetization segment in a recording medium 7 penetrates into a front intermediate core 3, then passes through an upper core 5, a rear intermediate core 4 and a lower core 2 and returns to an S pole of the magnetization segment, thus a magnetic closed circuit is obtained. An output voltage from the thin film magnetic head is obtained in proportion to the magnetic flux change per unit time which passes through a coil 9 and an amount of the magnetic flux 8 passing through the magnetic closed circuit.
When a magnetic material having a low relative permeability is employed as the magnetic head cores forming a magnetic circuit, and the upper core 5 and the lower core 2 are disposed facing closely to each other, a part of the magnetic flux 8 passes through a space between the upper and lower cores 5, 2 as a leakage flux 8a to make a short magnetic closed circuit, which poses a decrease of the output voltage of the thin film magnetic head.